1. Field of the Invention
The present invention relates to diaphragm control devices for cameras, and in particular to such diaphragm control devices in which scene light is measured through a diaphragm aperture in the process of being stopped-down and wherein the diaphragm closing operation is terminated in response to a control signal representing that the measured light intensity has attained a reference level established as a function of photographic exposure parameters such as shutter speed and film speed.
The invention has particular application to mirror release mechanisms used in conjunction with the above type of diaphragm control devices in single lens reflex cameras, and in particular to the above combination of mirror release mechanisms and diaphragm aperture control devices for selected timing release of the reflex mirror subsequent to aperture determination dependent upon whether the diaphragm is to be fully open or reduced.
2. Description of the Prior Art
In diaphragm control devices of the aforementioned type, it is desired that the diaphragm aperture is left fully open when the measured light intensity is equal to or exceeds an established reference level before the diaphragm stopping-down operation is actuated. However, it has been difficult for prior art camera diaphragm control devices to provide such a fully open diaphragm aperture in such cases. This is assumed to be due to the fact that a slight time lag is unavoidable from the generation of the control signal for actually arresting the diaphragm, such that the diaphragm is stopped-down a little further than is necessary during the aforementioned time lag. Additionally, the mechanical play among, and/or between, the various mechanical linkages from the diaphragm stopping-down control electromagnet to a diaphragm arresting member varies with individual devices. Also, the magnetic force required for pressing the armature of the electromagnet to its pole, for example, also varies from one to another of individual electromagnet mechanisms.